udp: fix rx queue len reported by diag and proc interface

After commit 6b229cf77d68 ("udp: add batching to udp_rmem_release()")
the sk_rmem_alloc field does not measure exactly anymore the
receive queue length, because we batch the rmem release. The issue
is really apparent only after commit 0d4a6608f68c ("udp: do rmem bulk
free even if the rx sk queue is empty"): the user space can easily
check for an empty socket with not-0 queue length reported by the 'ss'
tool or the procfs interface.

We need to use a custom UDP helper to report the correct queue length,
taking into account the forward allocation deficit.

Reported-by: trevor.francis@46labs.com
Fixes: 6b229cf77d68 ("UDP: add batching to udp_rmem_release()")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/transp_v6.h

@@ -45,8 +45,15 @@ int ip6_datagram_send_ctl(struct net *net, struct sock *sk, struct msghdr *msg,
 			  struct flowi6 *fl6, struct ipcm6_cookie *ipc6,
 			  struct sockcm_cookie *sockc);
 
-void ip6_dgram_sock_seq_show(struct seq_file *seq, struct sock *sp,
-			     __u16 srcp, __u16 destp, int bucket);
+void __ip6_dgram_sock_seq_show(struct seq_file *seq, struct sock *sp,
+			       __u16 srcp, __u16 destp, int rqueue, int bucket);
+static inline void
+ip6_dgram_sock_seq_show(struct seq_file *seq, struct sock *sp, __u16 srcp,
+			__u16 destp, int bucket)
+{
+	__ip6_dgram_sock_seq_show(seq, sp, srcp, destp, sk_rmem_alloc_get(sp),
+				  bucket);
+}
 
 #define LOOPBACK4_IPV6 cpu_to_be32(0x7f000006)
 

include/net/udp.h

@@ -247,6 +247,11 @@ static inline __be16 udp_flow_src_port(struct net *net, struct sk_buff *skb,
 	return htons((((u64) hash * (max - min)) >> 32) + min);
 }
 
+static inline int udp_rqueue_get(struct sock *sk)
+{
+	return sk_rmem_alloc_get(sk) - READ_ONCE(udp_sk(sk)->forward_deficit);
+}
+
 /* net/ipv4/udp.c */
 void udp_destruct_sock(struct sock *sk);
 void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len);

net/ipv4/udp.c

@@ -2772,7 +2772,7 @@ static void udp4_format_sock(struct sock *sp, struct seq_file *f,
 		" %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %d",
 		bucket, src, srcp, dest, destp, sp->sk_state,
 		sk_wmem_alloc_get(sp),
-		sk_rmem_alloc_get(sp),
+		udp_rqueue_get(sp),
 		0, 0L, 0,
 		from_kuid_munged(seq_user_ns(f), sock_i_uid(sp)),
 		0, sock_i_ino(sp),

net/ipv4/udp_diag.c

@@ -163,7 +163,7 @@ static int udp_diag_dump_one(struct sk_buff *in_skb, const struct nlmsghdr *nlh,
 static void udp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
 		void *info)
 {
-	r->idiag_rqueue = sk_rmem_alloc_get(sk);
+	r->idiag_rqueue = udp_rqueue_get(sk);
 	r->idiag_wqueue = sk_wmem_alloc_get(sk);
 }
 

net/ipv6/datagram.c

@@ -1019,8 +1019,8 @@ exit_f:
 }
 EXPORT_SYMBOL_GPL(ip6_datagram_send_ctl);
 
-void ip6_dgram_sock_seq_show(struct seq_file *seq, struct sock *sp,
-			     __u16 srcp, __u16 destp, int bucket)
+void __ip6_dgram_sock_seq_show(struct seq_file *seq, struct sock *sp,
+			       __u16 srcp, __u16 destp, int rqueue, int bucket)
 {
 	const struct in6_addr *dest, *src;
 
@@ -1036,7 +1036,7 @@ void ip6_dgram_sock_seq_show(struct seq_file *seq, struct sock *sp,
 		   dest->s6_addr32[2], dest->s6_addr32[3], destp,
 		   sp->sk_state,
 		   sk_wmem_alloc_get(sp),
-		   sk_rmem_alloc_get(sp),
+		   rqueue,
 		   0, 0L, 0,
 		   from_kuid_munged(seq_user_ns(seq), sock_i_uid(sp)),
 		   0,

net/ipv6/udp.c

@@ -1523,7 +1523,8 @@ int udp6_seq_show(struct seq_file *seq, void *v)
 		struct inet_sock *inet = inet_sk(v);
 		__u16 srcp = ntohs(inet->inet_sport);
 		__u16 destp = ntohs(inet->inet_dport);
-		ip6_dgram_sock_seq_show(seq, v, srcp, destp, bucket);
+		__ip6_dgram_sock_seq_show(seq, v, srcp, destp,
+					  udp_rqueue_get(v), bucket);
 	}
 	return 0;
 }